Dip painting apparatus and method



Dec. 5, 1961 c. E. PFLUG DIP PAINTING APPARATUS AND METHOD 5 Sheets-Sheet 1 Filed Deo. 8, 1958 INVENTOR.

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CHARLES E. PFLUG v /4 TTOE/VEY INVENTOR.

Dec. 5, 1961 c. E. PFLUG DIP PAINTING APPARATUS AND METHOD 5 Sheets-Sheet; 2

Filed Dec. 8, 1958 CHAELES E PFLUG ATrQe/vsy Dec. 5, 1961 c.'E. PFLUG DTP PAINTING APPARATUS AND METHOD 5 Sheets-Sheet :5

Filed Dec. 8, 1958 ZAL . INVENTOR. CHARLES E. PFL-UG Q@ /l/M Dec. 5, 1961 c. E. PFLUG 3,011,914

DIP PAINTING APPARATUS AND METHOD Filed Dec. 8, 1958 5 Sheets-Sheet 4 NVENTOR.

Cf/AEL E5 E. PFL 06 Dec. 5, 1961 c. E. PFLUG 3,011,914

DIP PAINTING APPARATUS AND METHOD Filed Dec. 8, 1958 5 Sheets-Sheet 5 @Aff kp. 70 .ZZ as INVENTOR. CHABL E5 E. PFLUG 7TOENEY United States Patent O 3,011,914 DIP PAINTING APPARATUS AND METHD Charles E. Pflug, Kenosha, Wis., assigner to American Motors Corporation, Kenosha, Wis., a corporation of Maryland Filed Dec. 8, 1958, Ser. No. 778,916 6 Claims. (Cl. 117-113) The invention relates to a method and apparatus for dip painting large objects such as automobile bodies.

The principal object is to control the iiow characteristics of the paint on the object after same has been withdrawn hom the dip tank, whereby a coating of uniform thickness and free from sags and runs is obtained.

In dip painting a large obiect with a type of liquid paint having as one of its ingredients `a rather volatile vehicle possessing a general-ly high evaporation rate, surface evaporation of the vehicle from the painted object may be too rapid wherein a skin is formed and the -liquid pm'nt beneath the skin continues to flow (during the draining period) causing a build-up of excess paint beneath the skin-this build-up being referred to as a sag The objective, then, is to promote the proper conditions under which the excess paint on the painted object will continue to ow during a predetermined period of time under conditions in which the surface evaporation rate is controlled to prevent sagging and to achieve a smooth coating of substantially uniform thickness throughout.

Thus, one specific object of the invention is to eect a control of the rate of surface evaporation so that all of the excess paint is permitted to flow from the painted object during the draining period.

Another object is to maintain the paint owage in a singular direction during the draining period.

A further specic object is to provide a tunnel within which the dip tank is situated-such tunnel being of a generally minimum cross-sectional area with reference to the object to be painted. Thus the paint vehicle vapors in the area surrounding the painted object are confined within as small a cubic volume area as is practical and such vapors are concentrated so as to saturate the atmosphere thereby retarding the rate of surface evaporation of the paint vehicle from the painted object and thereby permitting the excess paint to continue ilowing on the painted object a desired amount of time without incurring sags.

A further specific object is to provide a tunnel having entry and exit portions at opposite ends of the dip tank, each of which tare inclined at an angle with reference to the door line in the manner of a V, the dip tank being situated at the apex of the V. The paint vehicle is of a type which, when in a gaseous state, is heavier than the atmosphere and consequently becomes trapped largely within the apex area of the V, thus affording a heavier concentration of the vehicle vapors in the area where the painted object emerges from the dip tank. The degree of concentration of such vehicle vapors progressively decreases as the painted object proceeds up through the exit portion of the tunnel.

A further object is to provide a tunnel having means associated therewith for selectively adding ingredients to the atmosphere within ythe tunnel in the 'area surrounding the painted object and thereby aiding in controlling the flow characteristics of the excess paint on the painted object. For example, the addition of another gas which will tend to displace the air in the area surrounding the painted object, will serve to redu the amount of vehicle evaporated from the painted objectthis being accomplished by lowering the capacity of the atmosphere to absorb such Vehicle vapors. Such an added gas could be CO2, CO or. other similar gases which will not support 3,011,914 Patented Dec. 5, 1961 ice combustion and/or which will not absorb the vehicle vapors. Or it may be desirable to add water vapor in the form of steam or high humidity air to the atmosphere within the tunnel and thereby reduce the amount of vehicle vapors which the air can absorb due to the combination of vapor pressure caused by the water vapor and the paint Vehicle vapor.

A still furtherv lobject is to provide means associated with the tunnel for expediting the evaporation of the paint vehicle on the painted object yafter the paint has been properly distributed on the surface of the object in the thickness desired-this being accomplished by substantially removing the gas or water vapor as well as the vehicle vapor from the area surrounding the painted object and thereby expediting evaporation of the paint vehicle from the painted object.

A further object is to provide means for substantially preventing escape of the vehicle vapors into that portion of the tunnel leading up to the dip tank, such means also serving for eifecting cooling of the vobject to be painted as it approaches the dip tank.

A further object is to provide a dip painting apparatus having a paint circulation system wherein the likelihood of accumulation of surface scum and any other dirt particles in the paint is greatly lessened.

Other objects and advantages of the invention will be apparent from the ensuring specication and from the drawings in which:

FIG. 1 is a schematic plan View of la painting system incorporating the inventive subject matter with certain details omitted.

FIG. 2 is a schematic side elevational View of a portion of the system of FIG. l taken from the side thereof as indicated by the line 22.

FIG. 3 is a schematic sectional View through the tunnel, taken on the line 3-3 of FIG. 2 and with certain details omitted.

FIG. 4 is a schematic sectional view through the vtunnel, taken on the line 4 4 of FIG. 2 and with certain details omitted. v

FiG. 5 is a schematic sectional View taken on the line 5-5 of FIG. 2..

FG. 6 is a detailed schematic sectional View. of the dip tank and associated plumbing taken on the line 6 6 of FIG. 7.

FIG. 7 is a schematic plan view, broken in section, of the dip tank and certain associated parts.

FIG. S is a schematic sectional view of the lower portion of the cooling tunnel adjacent the dip tank.

FIG. 9 is a fragmentary sectional detail view of a portion of the cooling tunnel generally remote from the dip tank.

FIG. l() is a schematic sectional view of the tunnel taken on the line 10--10 of FIG. 2.

FIG. ll is a schematic sectional detail viewv of the tunnel taken on the line 11-11 of FIG. 2. i

F IG. 12 is a fragmentary sectional detail view of a typical portion of the tunnel taken on the line 12-12 of HG. 1.

FIG. 13 is a fragmentary sectional detail view of a typical portion of the cooling tunnel and taken onfthe line 13-13 of FIG. 2.

FIG. 14 is a fragmentary sectional detail view of a portion of the cooling tunnel taken on Ithe line 14-14- of FIG. 2.

FIG. 15 is an enlarged fragmentary sectional detail View taken on the line 15-15 of FIG. l2.

At the outset it should be noted that many views of the drawings are of a schematic nature-the intention being to generally illustrate the vdetails of the inventive subject matter rather than to present a true pictorial reproduction of the commercial embodiment thereof. For eX- ample, the comercial embodiment of the plumbing associated with the dip tank contemplates the use of various types of ttings for interconnecting various tributary pipes with main pipes and the details of such fittings are shown schematically. vAlso, various air ducts and fittings therefor are shown schematically for simplifying an understanding of the invention.

Additionally, no attempt has been made in the drawings tol followra given scale-for example, the wall thicknesses of the'panels which make up the tunnel Walls are greatly exaggerated in proportion to the actual size of the tunnel. The same is true of the wall thicknesses of the air ducts and the plumbing pipes and other parts of the inventive subject matter.

In general the apparatus for effecting the dip painting comprises a closed cooling tunnel A leading up to a paint filled dip tank B of sufficient depth to permit complete submergence of the object to be painted C (hereinafter sometimes identified as an automobile body). The dip tank is situated interiorly of the enclosed tunnel portion D which is connected to the closed exit or drip tunnel E. The automobile bodies are suspended from an endless conveyor F and move continuously through the tunnel at a predetermined rate of speed, each such body being submerged in the liquid paint contained in the dip tank B and then'ernerging therefrom-the excess paint draining by gravity from such bodies while they are travelling up through the exit tunnel E.

Referring to FIG. 1 there is shown a plan view of a suitable painting system incorporating the inventive subject matter and such a system includes a section of tunnel H Within which the automobile body C undergoes a treatment known in the trade as bonderizing (an undercoating which precedes the prime paint coating)-in a complete body treatment system the body would undergo cleaning before being bonderized After bonderizing, the body travels through an oven K before entering the cooling tunnel A. After the body leaves the drip tunnel E, it passes through tunnel section L (which lies in a horizontal plane) where the painted body continues draining the excess paint to some extent from the lowermost areas of the body. The body then enters an enlarged tunnel area M where any minor touch up or correcting work is done, after which it enters a painting booth N where additional spray painting of certain critical areas is accomplished (in an automobile body it is desirable to add an extra prime coat of paint under the Wheel housings). The body then passes through an oven O. Following this the body undergoes application of a finishing coat of paintthe apparatus for accomplishing this not being shown herein, since it forms no part of the inventive subject matter.

The entry or cooling portion of the tunnel A may be inclined at -an angle of approximately 30, plus or minus 5 with reference to the horizontal oor line 10. The tunnel section A is a continuation of the tunnel section K and the first break in the continuity of the tunneling occurs at S. Commencing at the location S, the tunneling is closed and continuous through the'successive tunnel sections K, A, D, E, L, M, N and the oven O. The tunnel section A serves as a cooling tunnel as will be explained more fully hereinafter.

The cooling tunnel merges with the horizontal tunnel section D which is situated directly above the dip tank B. The tank is, of course, open at the top and the side walls of the tank in conjunction with the side Walls of the tunnel section D form a closed tunnel above the dip tank preventing escape of vapors 'except within the interior of such tunnel.

The exit end of the tunnel D merges with the exit or drip Itunnel Ewhich is inclined at an angle of approximately 30, plus or minus 5, with reference to the horizontal floor line 10. The exit tunnel merges with the closed horizontal tunnel section L as previously explained.

The paint in the dip tank is, of course, in liquid form and of a predetermined viscosity. The paint formula includes as some of its ingredients a pigment along with a liquid vehicle which carries the pigment-the vehicle including a suitable paint thinner which evaporates into the atmosphere at a rate which is dependent upon the conditions existent in the atmosphere. The paint is continuously circulated by means of a pump i3 which receives the paint from the over-flow tank i4 and pumps same through suitable pipes 15 which open into the dip tank at or just above the floor level 10a thereof. Thus the fresh paint enters the dip tank near the bottom thereof and leaves the dip tank at the level of the paint within such dip tank through the drain openings 16 which are cut in the side walls of the tank and which communicate with the return pipes 17 leading to the over-flow tank 14. The drain openings are large enough to pass any'rnaterial that might be iioating on the surface of the paint.

FIGSQ., 5, 6 and 7 Vdisclose the plumbing details in a schematic manner. There are two sets of drain openings 16 and 16a, either set of which may be selected, depending upon the desired paint level in the dip tank. The lowerrnost set of openings 16a are closed oi by any suitable means (not shown) when it is desired to raise the paint level to the uppermost set of openings 16. Individual pipe sections 17a connect the openings 16 with the primary drain pipes 17. It will be noted that a primary drain pipe is provided at each of the side walls of the dip tank since there are similar sets of drain openings on each side of the tank. Each of the drain pipes 17 may communicate with the trunk line 17C leading to the over-how tank 14. The end Walls of the dip tank may be provided with sets of drain openings served by the tributary drain pipes 17a'. A number of'paint inlet openings may be provided as shown in FIGS. .6 and 7, a series of such openings 15a being situated in each of the side walls of the tank and additional openings 15b and 15C being situated in the floor and in the inclined end Walls respectively of such tank. The openings 15a are served by primary feed pipes 15d extending alongside of the tank side walls. The openings 15b and 15C are served by the principal feed pipe 15 through tributary pipes 15e, 15j, 15g, 15h, 15j and 15k, as shown in `FIG. 7. The pipes 15d may be served by the pipes 15g and 15h. The trunk pipe 15, as has previously been pointed out, leads to the pump 13. The inlet openings in the oor and in the end walls of the tank are preferably provided with housings 15m which are in the form of half cylinders, closed at one end, for directing the oW of the paint as it enters the tank in the desired directions as indicated by the various arrows in FIG. 7.

The over-flow tank has filters therein (not shown) which filter Athe paint coming from the dip tank before such paint is returned to the dip tank Via the pump 13 and pipes 15. A dump tank 18 is situated beneath the dip tank and also beneath a fire proof floor 19 which Serves as the floor of the tire proof pit 20 within which the dip tank is received. The dip tank and the associated tunnel D is preferably housed within a tire proof enclosure identified generally by the numeral 21. The dump tank 18 is provided with a vent pipe 22 which preferably exhausts at '23 outside of the enclosure 21. The dip tank is provided with a number of emergency drain openings 24 which are situated in the tank oor and which communicate with the drain pipe 24a which opens into the dump tank. The drain pipe 24a is provided with control valves 25 which are opened in response to a predetermined temperature condition within the tunnel D by means of temperature responsive apparatus not shown herein. In the event of a tire occurring within the tunnel D, the rise of temperature within the tunnel occasioned by the ames would result in the opening of the valves 25 and the consequent draining of the paint from the dip tank into the dump tank within the space of a few minutes.

In order to prevent, as nearly as possible, the movement of the paint vehicle vapors up through the tunnel section A, a stream of forced air is directed into the tunnel in the area adjacent to the entry end of the tunnel section D. Referring to FIGS. 8 and 9 the lloor of the tunnel may be provided with a suitable opening 26. A portion of the air passing through opening 26 travels directly into the tunnel through opening 26a and the remaining portion travels into the duct 27 which extends along the floor of the tunnel, terminating in the vicinity of the exhaust stack 28. The upper wall 29 of the duct is provided with a series of discharge openings 39 throughout its length (as best viewed in FIG. 8) for discharging cooling air from the blower 31 into the interior of the tunnel to assist in cooling the automobile bodies as they pass through the tunnel section A. The blower 31 may be housed within an enclosure 31a which has filters 3112 for filtering the air entering the enclosure under the inducement of the blower. The blower directs forced air through the enclosure wall opening 31e and thence through opening 26 as previously described.

An additional duct 3'2'extends along the roof'of the tunnel section A communicating with the exhaust stack 28. This exhaust duct is likewiseprovided with a series of openings 33 (as best viewed in FIG. 9) to receive the air within the tunnel, after it has passed over the automobile bodies, for eventual discharge through the stack 28. Each of the duct openings and each of the duct openings 33 is controlled by a damper 34 for selectively closing off as many openings as desired in effecting control of the air flow through the tunnel A. Only one of such dampers, for illustration purposes, is shown in FIG. l3-it being understood that similar dampers will be provided for each of the openings shown in HGS. 13 and 14.

Since the air which is traveling through tunnel A toward stack 28 becomes heated when passing the automobile bodies, the normal direction of ow is upwardly into the stack 28--the ow being enhanced by the conventional venturi effect at the outlet 28a of the stack. The blower 31, of course, contributes to the air ow through the tunnel A and the stream of air which is directed into the tunnel through the opening 26 will bey sufficiently turbulent as to interfere with and substantially prevent movement of the vapors from the tunnel section D into the tunnel section A. The concentration of the paint vehicle vapors is desired within the tunnel section D and within a portion of the exit tunnel E but not in tunnel A as will be more fully explained hereinafter.

The tunnel section E is provided with fresh air and exhaust ducts 35, 36, 37 and 38 respectively at each of its side walls--such ducts preferably extending throughout the full length of the tunnel section. The tunnel section L is likewise provided with fresh air and exhaust ducts a, 36a, 37a and 38a respectively of a construction similar to those in the tunnel section E (see FIG. 2)- such ducts preferably extending throughout the length of the tunnel section, as indicated in dotted lines in FIG. l. With reference to tunnel section D, both the front and rear walls of which are provided with doors 39, 39a and 39b (the rear wall doors not being shown), the ducts are arranged as follows. The exhaust (lower) duct in each wall is in two sections 40 and 41-one section on either side of the center door 39a. On either side of the center door the exhaust duct of each section extends up at 40a and v41a to the roof of the tunnel and opens into the ducts 40b and 41b which extend across the tunnel exteriorly thereof and open into a common exhaust duct 42 leading to the blower 43. A discharge duct 60a may extend from the blower 43 to atmosphere at 60b so that the vapors are exhausted outside of the building. Each fresh air duct in the front and rear walls is likewise in two sections, each section commencing at its respective end door and terminating short of the respective side edges of the center door. 'I'he fresh air duct sections on one side of the center doors open into the duct 44 and those on the other side open into duct 45. The principal duct 46 supplies each of the ducts 44 and 4S.

Each of the fresh air ducts within the tunnel sections D, E and L is provided with a series of openings 47 (see FIGS. l0, l2 and 15) situated near the roof of the respective tunnel sections and being spaced apart about 30 inches, more or less. The openings are provided throughout the length of the respective ducts and each such opening is provided with a suitable damper 48 for selectively opening or closing olf communication between the interior of the duct and the interior of the tunnel through that particular opening. A damper illustrative of the type employed with each opening is shown in detail in HG. l5, such damper being operable exteriorly of the tunnel by means of a suitable handle 49. The fresh air ducts and the openings 47 thus permit the entry of fresh air into the interior of the tunnel sections D, E. and L at any of a wide range of locations within such tunnels.

Each of the exhaust ducts within the tunnel sections D, E and L are likewise provided with openings 47a situated near the iloor level of the tunnel sections so that vapors or other gases within the interior of the tunnel sections can be exhausted therefrom at a low level. Since the paint vehicle vapors within the tunnel are heavier than air, they will be most greatly concentrated near tunnel oor level and hence will be most effectively withdrawn rom the tunnel with floor level exhaust openings. Each oneV of the exhaust openings 47a is provided with a damper of the type shown in FIG. l5 for selectively closing oil the opening (as has been explained hereinbefore With reference to the air inlet openings). The addition of moisturized air into the tunnel or the exhausting of vapors from the interior of the tunnel will depend upon several factors, the overall objective being to condition the atmosphere within the tunnel sections D and E in such a manner as to obtain the desired tlow characteristics of thepaint on the automobile body after it emerges from the dip tank.

On some days the humidity of the atmosphere will be considerably higher than on other days and the temperature of the atmosphere during the summer months will, of course, differ from the temperature during winter months. The atmospheric conditions will determine the use or non-use of the yfresh air and exhaust ducts or portions thereof.

The paint mixture likewise is a factor which must be taken into consideration particularly with reference to the evaporation rate of the paint vehicle and the viscosity of the paint. Under conditions in which the atmosphere has relatively low humidity and above normal temperatures, it may be desirable to lower the rate of evaporation of the paint vehicle vapors within the tunnel sections D and E, in which case the addition of water vapor can be eifected by opening several of the dampers in the fresh air ducts to permit the water vapor to enter the interior of the tunnels. A blower 52 may be situated at the entrance of the main fresh air inlet duct 46 and steam may be introduced into such duct from a suitable source (not shown) through the pipe 53, valve 54 and pipe 55. The steam will be carried along through the main duct 56 and enter the tunnel ducts 35 and 36 through duct 56a at inlet point 57 or at the inlet point 58. If the dampers in the ducts 35 and 36 are open, then the steam will enter the tunnel E at the various inlet openings 47 throughout the length of the tunnel. lf some or all of the dampers in the fresh air ducts in tunnel D are open then the steam will be carried through duct 46 to branch ducts 44 and 45' and thence into the interior of tunnel D. The exhaust ducts 37 and 38 open into the exhaust duct 60 at the lower end of the tunnel section E and also at the locations 61 and 62 with the exhaust duct 63. A suitable blower 64 pulls the exhaust ail through the duct 63 7 and blower 43 pulls Vthe exhaust air through the ducts 42 and 60 yfrom whence they may be exhausted through a suitable stack not shown.

The addition of Water vapor into the tunnel in the vicinity of the painted object will lower the evaporation rate of the paint vehicle vapors by reducing the amount of the vehicle vapors which the air within the tunnel can absorb due to the combination of vapor pressure caused by the Water vapor and the paint vehicle vapors. The addition of another form of gas, which will tend to displace the air, will also reduce the amount of paint vehicle evaporated from the painted object and this type of gas may be CO2, CO or other similar gases which will not support combustion and/or which will not absorb the paint vehicle vapors. In some instances it may be desirable to slow up the evaporation rate of the vehicle vapors near the lower end of tunnel E and as the painted object nears the upper end of such tunnel, it may be desirable to speed up the evaporation rate, in which case exhausting through ducts 37 and 38 may take place near the upper end of the tunnel while additives are being introduced through ducts 35 and 36 near the lower end of the tunnel. Y

By inclining the drip tunnel E, the'excess paint drains in a path which is generally diagonally across the automobile body toward the rear end thereof. The length of the inclined drip tunnel is such that most of the draining of the excess paint from the automobile body is completed sufiiciently to prevent the formation of sags and while the automobile body is traveling up through the drip tunnel at a constant angletof inclination, the excess paint flows across the body in a singular direction, thereby further preventing the possibility of sags The direction of flow of the excess paint across the automobile vbody is, of course vertical, being occasioned as the result of gravity, and when the automobile body reaches the point where it commences to enter the horizontal tunnel section L, then any further paint flowage would be in a different direction relative to the body due to changing l the position of the automobile body into a horizontal path. The' excess paint, however, has been suiciently drained from the automobile body prior to its shifting from an inclined position into a horizontal position as it enters tunnel L. Any drainage that takes place Within tunnel L simply involves a minor amount of excess paint which is situated at the lowermost edges of the automobile body.

The floor area of the drip tunnel E and the Hoor area ofrtunnel section L is preferably provided with coverings (not shown) for catching the excess paint drippings such coverings being replaceable periodically as desired.

As previously mentioned herein the automobile bodies are suspended from an endless conveyor and move through the various tunnel sections at a predetermined rate of speed. Referring to FIGS. 2, 3, 4, 10 and ll there is shown one form of conveyor apparatus which includes a stationary rail 7i) which may be secured to( the roofsof the various tunnel sections substantially midway between the side walls thereof. Each automobile body is removably carried by a xture 71 which has suitable rollers 72 which ride on the rail 70 as best shown in FIGS. 3 and 4.

Viewing FIG. 2 it will be noted that only two automobile bodies C are shown (in dotted lines)-it being understood that during normal operation there will be a large number of such bodies suspended from the conveyor in successive fashion substantially equally spaced from each 'other as they progress through the succession of tunnels H through G.

The tunnel section L, as has been briefly explained hereinbefore, is provided with fresh air intake ducts a and 36a and exhaust ducts 37a and 33a of the typewhich have previously been described in detail in connection with tunnel section E. These fresh air intake ducts and exhaust ducts are likewise providedwith a 8 series of inlet and exhaust openings similar to the openings 47 and 47a respectively as shown best in FIG. l2 each of which is controlled by a damper of the type shown in FIG. l5. These inlet and exhaust openings and the dampers therefor operate in the same manner and serve the same functions as has previously been explained with reference to the corresponding components of tunnel sections D and E. The fresh air intake ducts may be served with a primary duct 75 and a blower 76 may be provided for pushing the fresh air supply through duct 75 and on into the tunnel ducts 35a and 36a. A suitable conduit 53a, valve 54a and conduit 55a may be utilized to serve the same functions as the corresponding components 53, 54 and 55. lt will be understood that the conduit 53 and valve 54 could be arranged so as to additionally serve the duct 75,7if desired, The exhaust ducts 37a and 38a may communicate with a primary exhaust duct 77 and a blower 78 may be utilized for pulling the exhaust air from the interior of the tunnel section L in the same manner as has been explained with reference to the exhausting of the air from the ducts 37 and 38 in tunnel section E.

it has been previously explained that the paint within the dip tank is continuously circulated, being drained from the tank through drain pipes 17 and reentering the tank through the inlet pipes 15. By introducing the paint into the dip tank near the floor level thereof and then draining the paint from the dip tank at the surface level of the paint, it is possible to substantially prevent the formation of any scum at the upper surface of the paint within the dip tank, thereby assuring that a minimum of foreign material will be deposited on the automobile bodies as they emerge from the dip tank. The introduction of the'paint at oor level also minimizes the possiy bility of sludge formation on the tank floor.

Under some conditions of operation it is not necessary to utilize the inlet air ducts or the exhaust ducts-all of the dampers in tunnels D and E therefore being closed. Under such conditions it is necessary to retard the evaperation rate of the paint vehicle on the painted object after it emerges from the dip tank. This can be accomplished by restricting the cubic volume of the interior of the tunnel-particularly in the area above the dip tank and in drip tunnel E-to a relatively small area so as to adequately eoniine the evaporated paint vehicles. The degree of saturation of the atmosphere in the inte rior of tunnel sections D and E with vehicle vapors is such that the rate of evaporation of the paint vehicle from the surface of the painted object is retarded, thereby permitting the excess paint on the object to continue flowing until the desired coating free of sags'and of substantially uniform thickness is obtained. The V shape presented by the combined tunnel sections A, D and E assures that the degree of saturation of the atmosphere with vehicle vapors is greatest within tunnel section D and at the lower end of tunnel section E-such vehicle vapors being heavier than air and thus concentrating more heavily at the lower levels within the tunnel. The rate of evaporation is thus slower where the painted object emerges from the dip tank than, for example, at the upper end of tunnel section E. By the time the painted object reaches the upper end of tunnel section E the rate of evaporation increases as has been previously explained herein.

In an installation for painting automobile bodiesit has been found that a tunnel having inside dimensions of approximately 8 feet in heighth and 8 feet in width will provide the necessary confined area for effecting the required vehicle vapor saturation of the atmosphere within the tunnel. It will be understood that the cubic volunie of a given length of object to be painted in'proportion to the cubic volume of a comparable length of tunnel will vary considerably in accordance with whether the object to be painted is of a hollow nature or of solid construction. Thus in the case of an automobile body (which is of hollow construction) the cubic volume of area displaced thereby would be several times less than the cubic volume of a section of tunnel equal in length to the length of the automobile body. It is, of course, necessary to provide a tunnel with a cross sectional area sufficient to accommodate the external dimensions of the object being painted even though the cubic volume displaced by such object might be several times less than the cubic Volume of a given length of the tunnel accommodating such object. The general objective is to conne the cross sectional area of the tunnel as much as is reasonably possible,

Referring to FIGS. 2 and 5 it will be understood that the structure which supports the conveyor rail 70 must project downwardly into the interior of the tunnel section D in order that the automobile body being painted can be submerged into the paint in the dip tank. Such structure may consist of suitable beams 70a and 70b which carry the hanger structure 70e to which the rail 70 is secured. The path which the rail 70 follows within the tunnel section D is generally indicated in dotted lines in FIG. 2.

I claim:

l. A method of applying a coating of paint of substantially uniform thickness onto the surface areas of a comparatively large object, such paint being in a liquid form and having as one of its ingredients a vehicle in liquid form and having an evaporation rate greater than water and such paint being stored in a reservoir and the reservoir being housed in a tunnel open at its ends, such tunnel having inclined entry and exit portions emanating from opposite ends of the reservoir and the entry and exit portions of the tunnel together with that portion of the tunnel housing the reservoir establishing an enclosed and confined area of the tunnel, such method comprising the steps of: moving the object to -be painted through the entry portion of the tunnel toward the reservoir; then immersing the object into the liquid paint in the reservoir; then withdrawing the object from the paint and moving it through the tunnel until the object is completely withdrawn out of the liquid paint in the reservoir; and then adding an ingredient in fluid form into the atmosphere within the tunnel to intermingle with such atmosphere for aiding in controlling the rate of surface evaporation of the vehicle of the paint on the object and simultaneously causing a concentration of the vehicle vapors which have evaporated from the vehicle in the paint in the reservoir to be trapped in the enclosed and confined area of the tunnel and continuing to move the object through the exit portion of the tunnel away from the reservoir.

2. A method of applying a coating of paint of substantially uniform thickness onto the surface areas of a comparatively large object, such paint being in a liquid form and having as one of its ingredients a vehicle in liquid form and having an evaporation rate greater than water and such paint being stored in a reservoir and the reservoir being housed in a tunnel open at its ends, such tunnel having inclined entry and exit portions emanating from opposite ends of the reservoir and the entry and exit portions of the tunnel together with that portion of the tunnel housing the reservoir establishing an enclosed and confined area of the tunnel, such method comprising the steps of: moving the object to be painted through the entry portion of the tunnel toward the reservoir; then immersing the object into the liquid paint in the reservoir; then withdrawing the object from the paint and moving it through the tunnel until the object is completely withdrawn out of the liquid paint in the reservoir; causing a heavy concentration of the vehicle vapors which have evaporated from the vehicle in the paint in the reservoir to be trapped in the enclosed and confined area of the tunnel; then adding water vapor into the interior of the tunnel for intermingling with the atmosphere and regulating the temperature conditions of the atmosphere withing the tunnel, whereby the rate of surface evaporation of the vehicle of the paint on the object is controlled within predetermined limits; and continuing to move the object through the exit portion of the tunnel away from the reservoir.

3. Apparatus for dip vpainting a large object comprising: an elongated tunnel having a vertex area and entry and exit portions each inclined upwardly and divergently from such area at an angle between 25 and 35 degrees; a reservoir in the tunnel and situatedl in the vertex area thereof; a supply of liquid paint in the reservoir and having as an ingredient a vehicle having a higher evaporation rate than water and after transformation into a gaseous form having a higher specific lgravity than air; means for retarding the rate of evaporation of the paint vehicle from the painted object after such object is withdrawn from the reservoir; said means including the trapping of the vehicle in a concentrated gaseous form within the vertex area of the tunnel and within the adjacent inclined entry and exit portions of the tunnel, such trapping being occasioned as -a result of the gaseous vehicle being heavier than air and the interior of the tunnel in the vertex area being at a lower level than la substantial portion of the interior of the inclined entry and exit portions of the tunnel, said elongated tunnel throughout the vertex area and throughout the inclined entry and exit portions normally being substantially closed for preventing escape of ygases from within the tunnel and blower means associated with the entry portion of the tunnel, the entry portion of the tunnel having an opening in one wall thereof for establishing communication between the blower means and the interior of the tunnel whereby forced air can be directed into the interior of the tunnel toward the Vertex area above the reservoir and into contact with the gaseous vehicle for retarding its flow from the vertex area into the inclined entry portion of the tunnel.

4. Apparatus for dip painting as set forth in claim 3 wherein the blower means also serves to provide a supply of cooling air into the entry portion of the tunnel for assisting in lowering the temperature of the object to be painted.

5. Apparatus for dip painting a large object comprising: an elongated tunnel having entry and exit portions each inclined upwardly and divergently from a vertex area at an angle between 25 and 35 degrees; a reservoir in the tunnel and situated in the vertex area thereof; a supply of liquid paint having as an ingredient a vehicle having a higher evaporation rate than water and after transformation into a gaseous form having a higher specic gravity than air; means for regulating the rate of evaporation of the paint vehicle from the painted object after such object is Withdrawn from the reservoir, said means including the trapping of the vehicle in a concentrated gaseous form within the vertex area of the tunnel and within the adjacent inclined entry and exit portions of the tunnel, such trapping being occasioned as a result of the gaseous vehicle being heavier than air and the interior of the tunnel in the vertex area being at a lower level than a substantial portion of the interior of the inclined entry and exit portions of the tunnel, said elongated tunnel throughout the vertex area and throughout the inclined entry and exit portions normally being substantially closed for preventing escape of gases from within the tunnel and said means also including inlet and exhaust ducts extending alongside of a wall of the tunnel, said tunnel wall having openings therein for establishing communication between the interior of the inlet and exhaust ducts and the interior of the tunnel, whereby an added ingredient in iluid form may be introduced into the interior of the tunnel via the inlet duct for intermingling with the atmosphere within the tunnel and whereby the atmosphere within the tunnel may be exhausted therefrom via the exhaust duct.

6. Apparatus as set forth in claim 5 wherein dempers are mounted in the ducts for selectively controlling the estabishing of communication betwen the interior of the ducts and the interior of the tunnel.

References Cited n the le of this patent UNITED STATES PATENTS Robertson Apr. 275, 1933 Robertson May 9, 1933 

1. A METHOD OF APPLYING A COATING OF PAINT OF SUBSTANTIALLY UNIFORM THICKNESS ONTO THE SURFACE AREAS OF A COMPARATIVELY LARGE OBJECT, SUCH PAINT BEING IN A LIQUID FORM AND HAVING AS ONE OF ITS INGREDIENTS A VEHICLE IN LIQUID FORM AND HAVING AN EVAPORATION RATE GREATER THAN WATER AND SUCH PAINT BEING STORED IN A RESERVOIR AND THE RESERVOIR BEING HOUSED IN A TUNNEL OPEN AT ITS ENDS, SUCH TUNNEL HAVING INCLINED ENTRY AND EXIT PORTIONS EMANATING FROM OPPOSITE ENDS OF THE RESERVOIR AND THE ENTRY AND EXIT PORTIONS OF THE TUNNEL TOGETHER WITH THAT PORTION OF THE TUNNEL HOUSING THE RESERVOIR ESTABLISHING AN ENCLOSED AND CONFINED AREA OF THE TUNNEL, SUCH METHOD COMPRISING THE STEPS OF: MOVING THE OBJECT TO BE PAINTED THROUGH THE ENTRY PORTION OF THE TUNNEL TOWARD THE RESERVOIR, THEN IMMERSING THE OBJECT FROM THE PAINT AND MOVING THEN WITHDRAWING THE OBJECT FROM THE PAINT AND MOVING IT THROUGH THE TUNNEL UNTIL THE OBJECT IS COMPLETELY WITHDRAWN OUT OF THE LIQUID PAINT IN THE RESERVOIR, AND THEN ADDING AN INGREDIENT IN FLUID FORM INTO THE ATMOSPHERE WITHIN THE TUNNEL TO INTERMINGLE WITH SUCH ATMOSPHERE FOR AIDING IN CONTROLLING THE RATE OF SURFACE EVAPORATION OF THE VEHICLE OF THE PAINT ON THE OBJECT AND SIMULTANEOUSLY CAUSING A CONCENTRATION OF THE VEHICLE VAPORS WHICH HAVE EVAPORATED FROM THE VEHICLE IN THE PAINT IN THE RESERVOIR TO BE TRAPPED IN THE ENCLOSED AND CONFINED AREA OF THE TUNNEL AND CONTINUING TO MOVE THE OBJECT THROUGH THE EXIT PORTION OF THE TUNNEL AWAY FROM THE RESERVOIR. 